Coating apparatus for sheet material

ABSTRACT

In an apparatus in which the thickness of a coating on sheet material is controlled by passing the material between a backing roll and a thin, rotating rod of a doctor blade assembly, the rod is rotatably embedded in a confined body of elastomeric polyurethane or synthetic rubber. A circumferential portion of the rod is exposed between two lips of the body which is under compressive stress between the confining walls and the rod. Lubricant and cooling liquid is fed to an axial groove open toward the receptacle of the body, mainly discharged axially from the groove and partly withdrawn by suction from another groove circumferentially spaced from the first groove in the direction of rod rotation.

0 United States Patent [151 3,701,335

Barnscheidt 1 1 Oct. 31, 1972 [54] COATING APPARATUS FOR SHEET 3,179,0334/1965 Warner ..118/104 MATERIAL 3,195,500 7/1965 Kuhnel ..118/104 X3,084,663 4 1963 Warner ..118/104 [721 Invenmrg namscheid" Smbeg/3,143,438 8/1964 Campbe1l ..113/104 3,031,872 5/1962 Kusters ..118/104ux [73] Assignee: Feldmuhle Aktiengesellschaft, Dus- 2,398,844 4/1946Muggleton et a1. ....1 18/262 X seldorf, Germany Primary ExaminerJamesKee Chi [22] 1971 Attorney-Kelrnan & Berman [21] App1.No.: 114,845

[57] ABSTRACT {30] Foreign Application Priority Data In an apparatus inwhich the thickness of a coating on sheet material is controlled bypassing the material f germany between a backing roll and a thin,rotating rod of a u y many doctor blade assembly, the rod is rotatablyembedded in a confined body of elastomeric polyurethane or g ffiggsynthetic rubber. A circumferential portion of the rod [58] Fie'ld 104 gH9 H0 is exposed between two lips of the body which is 118/203f15/2g6under compressive stress between the confining walls and the rod.Lubricant and cooling liquid is fed to an axial groove open toward thereceptacle of the body, [56] Rdercnces Cited mainly discharged axiallyfrom the groove and partly UNITED STATES pATENTS withdrawn by suctionfrom another groove circum- 2 695 004 11/1954 M t t I 8,262 ferentiallyspaced from the first groove in the i on gomery e a direction of rodrotation. 3,029,779 4/1962 l'lornboster ..118/104 3,021,307 2/1962Csendes ..260/72 9 Claims, 4 Drawing Figures PHENTED I973 3.701.335

FIGJ

WOLFGANG BAR SCH y Me MP Idem W PKTENTEU W I972 3.701.335

sum 2 BF 3 AGENTS COATING APPARATUS FOR SHEET MATERIAL This inventionrelates to coating apparatus for sheet material, and more particularlyto improvements in doctor blade assemblies and in their cooperation withother elements of coating machines.

In it more specific aspects, the invention is concerned with thecooperation between a backing roll tangentially a doctor blade whoseedge is constituted by an elongated rod member rotating about itslongitudinal axis while tangentally engaging coated sheet materialsupported by the backing roll.

The rod member is thin enough to be flexibleeven when made of stainlesssteel, the usual material of construction, and its spacing from thebacking roll must be maintained in a well-defined manner in order tocontrol the thickness of the coating on the sheet material.

It has been proposed in US. Pat. No.2,695,004 to have the rod membermounted in a cavity of a holder at least as flexible as the rod memberitself. The several portions of the rod member are held at a desireddistance from the backing roll by adjusting screws.

The recommended material of construction for the holder isfabric-laminated phenol-formaldehyde resin. While this material issomewhat flexible, and sufficiently so for the intended purpose, it doesnot yield under the pressure exerted by pigment particles whichunavoidably find their way to the bearing face of the holder normally incontact with the rod member. The pigment particles increase frictionbetween the holder and rod member, and cause relatively rapid wear.Tight sealing engagement between the relatively rigid holder and the rodmember cannot be maintained under such wear.

It has now been found that the durability of a doctor blade assemblyemploying a rotating rod member can be greatly increased, and otheradvantages can be gained by conformingly receiving the rotating rodmember in a receptable defined by a body of elastomeric materialconfined in a guide channel of much more rigid walls. The dimensions ofthe receptacle are chosen in such a manner that the receptacle issmaller transversely of the longitudinal axis of the rod member than thelatter when the rod member is removed, the arrangement being such thatthe body is in compressive strain between the rod member and theconfining walls.

Two lip portions of the body, which are elongated in the direction ofthe axis of rod rotation, bound the open side of the receptacle and aface in the receptacle which connects the lip portions and has acircumferential width relative to the axis of the rod member which issubstantially greater than 180.

Other features, additional objects, and many of the attendant advantagesof this invention will readily become apparent as the same is betterunderstood by reference to the following description of preferredembodiments when considered in connection with the ap-. pended drawingin which: I

FIG. 1 shows a coating apparatus of the invention in fragmentary sideelevational section;

FIG. 2 shows a portion of the apparatus of FIG. 1 on a larger scale andin more detail;

FIG. 3 illustrates a first modification of the apparatu of FIG. 1; and

FIG. 4 shows a second modification, the views of FIGS. 3 and 4 being ona scale similar to that of FIG. 2.

.width of the coating machine at right angles to the plane of FIG. 1,and such width will be understood to be many times greater than anydimension seen in FIG.

A stainless steel rod 3 of generally cylindrical shape is conforminglyembedded in the bar 2, and only a small circumferential portion of therod projects from a face of the bar which is directed outward of theopen side of the guide channel between the plates 1 and toward a rubbercoating 4 on the core 5 of a backing roll, the core essentiallyconsisting of steel or cast iron.

Only the piston rod 6 of a pneumatic jack is seen in FIG. 1. Thenon-illustrated cylinder is mounted or: the machine frame, and therebyfixedly connected with the plates 1. A transverse steel plate 6a on thefree end of the piston rod 6 in the guide channel abuttingly engages theface of the bar 2 directed away from the roll 5. It will be understood,that other jacks, not seen in the drawing are arranged along the plates1 as will presently be explained.

As is better seen in FIG. 2, a distributor conduit 7 connected to anon-illustrated water line extends through almost the full length of thebar 2. Multiple branch channels 8 extend from longitudinally spacedportions of the distributor conduit 7 at right angles toward the roll 5and connect the conduit 7 with three sets of orifices 9 in respectivegrooves 10 formed in a cylindrically arcuate inner face about areceptacle in the bar 2. The receptacle is practically filled with therod 3 in the assembled condition of the apparatus, and the elastomericmaterial of the bar 2 would expand and reduce the size of the receptacleif the rod 3 were removed.

The rod is enveloped by the inner face of the bar 2 in an arc of about300, and is normally rotated by a mechanism, not shown but known initself, in the direction of the curvedarrow in FIG. 2, which is op--posite to the direction of niovement of the backing roll, as indicatedby an arrow in FlG.l. The rod 3 moves toward an in glfll, acutelyangular, leading lip portion 11 ofthe bar-2 whichisfirmlyheldagainstthesurfaee of the steel rod 3 by stresses in the resilientlydeformed bar 2. Pigment particles are not likely to penetrate the sealformed bythe lip portion II. If they do, nopermanentdamagelsdonetothesealwhlehagaincloses hehind the pigmentparticles.

Water is fed through the distributor conduit 7 into the grooves 10 whichare trapezoidal in cross section and flare toward the receptaclecontaining the rod 3.

The obtuse angles formed between the arcuate inner face of the bar 2 andthe side walls of the grooves 10 facilitate entry of captured pigmentparticles into the grooves. They also prevent concentration of stressesin the relatively weak lip portion 11.

Most of the water supplied to the grooves 10 flows along the grooves andis ultimately discharged with the entrained pigment particles beyond thesides of the apparatus in a manner obvious and not specificallyillustrated. The flowing water keeps the lip portion 11 cool and therebyprotects it against wear to which this portion is most exposed duringnormal operation of the apparatus. Some water is carried as a thin filmalong the interface of the bar 2 and the rod 3 during the rotarymovement of the latter.

Water is an excellent lubricant for interfaces of most elastomers andstainless steel, but other lubricant and cooling liquids may be employedif the presence of water is not compatible with the coating materialapplied to the sheet material processed, or if the materials ofconstruction so require.

ln the modified apparatus of the invention partly illustrated in H63,and identical with that seen in FIGS. 1 and 2, as far as not explicitlyshown, a single flaring groove in the polyurethane bar 2' extends overthe entire working length of the rod 3 and is supplied with water orother lubricant and coolant from a branch channel 8 as described above.The liquid film formed at the groove 10 between the rod 3 and theresilient bar 2', generally closely similar to the bar 2, is carried ina cylindrically arcuate path by rotating bar 3 until it is almostcompletely removed at a groove 10 near the trailing lip portion 11' ofthe bar 2'. The groove 10' is a trapezoidal cross section and taperstoward the receptacle for the rod 3 so that it presents an acutelyangular edge 14 of the lip portion 11' to the moving rod 3. The edge 14wipes the liquid film from the rod surface, and the liquid collected inthe groove 10' is drawn off by a suction circuit of which only a branchconduit 13 is seen in FIG.3. The vacuum in the groove 10' enhances thecontact pressure between the edge 14 and the rod 3. No significantamounts of lubricant can reach the sheet material 12 which is beingengaged by the rod 3.

With some lubricants, particularly those having relatively highviscosity, the arrangement shown in FIG. 4 is preferred. Thepolyurethane elastomer bar 2", identical with or closely similar to thebars 2,2, as far as not illustrated, is formed with relatively large andwide grooves 100,102: respectively contiguous to the lip portionslla,llb which bound the open side of the receptacle for the rod 3. inthe instant case, the grooves are so dimensioned that they divide theinner arcuate face of the receptacle into a backing portion 15 and twomarginal portions between the acutely angular edges of the lip portionsand the grooves. -rooves. The marginal portions have each acircumferential width of about 30, and the backing portion 15 is about60 wide. FIG. 4 illustrates a limiting condition, and it is usuallypreferred that the two marginal portions of the inner receptacle facehave a combined circumferential width smaller than that of the faceportion between the grooves. Friction between the rod 3 and bar 2" isminimal.

As is better seen in FIGA, and has been omited from FIG. 1 for the sakeof clarity, the rubber coating 4 on the core 5 consists of two layerswhich are radially superimposed. The outer layer 17 consists ofrelatively hard rubber, and the inner layer 16 is much softer and itsradial thickness is much greater than that of the layer 17. Best resultsare obtained when the thickness of the layer 16 is four to ten timesthat of the layer 17, the thickness of the outer layer being evensmaller than the radius of the rod 3. The hardness of the elastomericmaterial in the bars 2,2',2" is chosen so that the outer layer 17 iswrapped about a part of the exposed face of the rod 3 withoutsignificant distortion of the embedding bar 3, as is shown in FIGA.

In typical coating apparatus of the invention, the polyurethane employedfor making the bars 2,2',2" had a Shore hardness of 90 95, the outerlayer 17 a hardness of 40 and a thickness of about 5 mm, and the innerlayer a hardness of 20. Generally, the Shore hardness of the eiastomericbodies 2,2',2 should not be less than 70", that of the outer layer 17between and 70, and that of the inner layer 10 to 30. Under theseconditions, the coated sheet material travels through a relatively longnip between the backing roll and the rod 3, as is evident from FIGA,without excessive wear of the relatively hard outer layer 17 whosethickness should be between 3 and 10 mm, depending on its hardnesswithin the range mentioned above.

Wear of the backing roll is also held to a minimum by the resiliency ofthe pneumatic jacks represented in FIG. 1 by the piston rod 6. The jacksare closely spaced along the bar 2, typically 5 cm apart, and arepreferably connected with a compressed air line by individual pressurereducing valves which permit close control of the force with which theseveral plates 6a urge the bar 2 to move in the guide channel betweenthe plates 1 toward the backing roll. Once the jacks are suitably ad- 30justed, the apparatus of the invention produces long runs of coatedpaper having an entirely uniform finish without any trace of striping inthe direction of paper movement through the coating apparatus.

The unitary polyurethane bars 2,2'2"2" have a long useful life. Ifrequired, they are replaced after fully retracting the piston rods 6 andwithdrawing the rod 3 between the resilient lips. A new bar is insertedby reversing the sequence of withdrawal operations.

Elastomeric materials other than polyurethane may be employed forembedding the rod 3, and wear resistant synthetic rubber has been usedto advantage in the bars 2,2',2".

Other changes and modifications in the apparatus of the invention willreadily suggest themselves to those skilled in the art, and it should beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than is specifically disclosed.

What is claimed is:

1. In a coating apparatus for paper and like sheet material including arotatable backing roll and a doctor blade assembly axially coextensivewith the roll, said assembly including an elongated rod member and aholder arrangement supporting the rod member for rotation about an axisextending in the direction of elongation of said rod member andsubstantially parallel to the axis of said roll while sheet materialbacked by said roll is engaged by said rod member, the improvement whichcomprises:

a. wall means in said holder arrangementdefining a guide channel opentoward b. a body of elastomeric material conformingly received in saidchannel,

1. said body defining therein a receptacle elongated in said directionand transversely open toward said roll, said receptacle confonninglyreceiving said rod member,

2. the transverse dimensions of said receptacle in the absence of saidrod member being smaller than the corresponding dimensions of said rodmember in such a manner that said body is under compressive stressbetween said wall means and said rod member,

3. said body having two lip portions elongated in said direction, saidlip portion bounding the open side of said receptacle, and a face insaid receptacle connecting said lip portions,

. the circumferential width of said face relative to said axis of therod member being substantially greater than 1 80.

2. ln an apparatus as set forth in claim 1, said face being formed withone groove adjacent one of said lip portions and remote from the otherlip portion, and with another groove adjacent said other lip portion andremote from said one lip portion, said grooves being elongated in saiddirection, means for supplying a liquid to said one groove, and suctionmeans for withdrawing said liquid from said other groove.

3. In an apparatus as set forth in claim 1, the resiliency of saidelastomeric material being sufficient to permit said rod member to bewithdrawn between said lip portions through the open side of saidreceptacle, and to be inserted between said lip portions into saidreceptacle.

4. In an apparatus as set forth in claim 2, said other lip portionhaving an acutely angular edge bounding said other groove, the othergroove tapering transversely toward said receptacle.

5. In an apparatus as set forth in claim 2, said lip portions havingrespective oppositely spaced edges, said edges and said groovescircumferentially bounding respective marginal portions of said face,the circumferential width of said face between said grooves being atleast equal to the combined circumferential width of said marginalportions.

6. In an apparatus as. set forth in claim 1, said body essentiallyconsisting of polyurethane or synthetic rubber.

7. In an apparatus as set forth in claim 1, said roll having asubstantially rigid core and two radially superposed layers ofelastomeric coating material on said core, the material of the outerlayer being substantially harder than the material of the inner layer,and the radial thickness of the inner layer being four to ten times theradial thickness of the outer layer.

8. In an apparatus as set forth in claim 7, said thickness of the outerlayer being substantially smaller than the radius of said rod member.

9. In an apparatus as set forth in claim 1, a plurality of pneumaticmotor means on said wall means yielding urging said body to move in saidchannel toward said roll.

1. In a coating apparatus for paper and like sheet material including arotatable backing roll and a doctor blade assembly axially coextensivewith the roll, said assembly including an elongated rod member and aholder arrangement supporting the rod member for rotation about an axisextending in the direction of elongation of said rod member andsubstantially parallel to the axis of said roll while sheet materialbacked by said roll is engaged by said rod member, the improvement whichcomprises: a. wall means in said holder arrangement defining a guidechannel open toward said roll; and b. a body of elastomeric materialconformingly received in said channel,
 1. said body defining therein areceptacle elongated in said direction and transversely open toward saidroll, said receptacle conformingly receiving said rod member,
 2. thetransverse dimensions of said receptacle in the absence of said rodmember being smaller than the corresponding dimensions of said rodmember in such a manner that said body is under compressive stressbetween said wall means and said rod member,
 3. said body having two lipportions elongated in said direction, said lip portions bounding theopen side of said receptacle, and a face in said receptacle connectingsaid lip portions,
 4. the circumferential width of said face relative tosaid axis of the rod member being substantially greater than 180*. 2.the transverse dimensions of said receptacle in the absence of said rodmember being smaller than the corresponding dimensions of said rodmember in such a manner that said body is under compressive stressbetween said wall means and said rod member,
 2. In an apparatus as setforth in claim 1, said face being formed with one groove adjacent one ofsaid lip portions and remote from the other lip portion, and withanother groove adjacent said other lip portion and remote from said onelip portion, said grooves being eloNgated in said direction, means forsupplying a liquid to said one groove, and suction means for withdrawingsaid liquid from said other groove.
 3. In an apparatus as set forth inclaim 1, the resiliency of said elastomeric material being sufficient topermit said rod member to be withdrawn between said lip portions throughthe open side of said receptacle, and to be inserted between said lipportions into said receptacle.
 3. said body having two lip portionselongated in said direction, said lip portions bounding the open side ofsaid receptacle, and a face in said receptacle connecting said lipportions,
 4. the circumferential width of said face relative to saidaxis of the rod member being substantially greater than 180*.
 4. In anapparatus as set forth in claim 2, said other lip portion having anacutely angular edge bounding said other groove, the other groovetapering transversely toward said receptacle.
 5. In an apparatus as setforth in claim 2, said lip portions having respective oppositely spacededges, said edges and said grooves circumferentially bounding respectivemarginal portions of said face, the circumferential width of said facebetween said grooves being at least equal to the combinedcircumferential width of said marginal portions.
 6. In an apparatus asset forth in claim 1, said body essentially consisting of polyurethaneor synthetic rubber.
 7. In an apparatus as set forth in claim 1, saidroll having a substantially rigid core and two radially superposedlayers of elastomeric coating material on said core, the material of theouter layer being substantially harder than the material of the innerlayer, and the radial thickness of the inner layer being four to tentimes the radial thickness of the outer layer.
 8. In an apparatus as setforth in claim 7, said thickness of the outer layer being substantiallysmaller than the radius of said rod member.
 9. In an apparatus as setforth in claim 1, a plurality of pneumatic motor means on said wallmeans yieldably urging said body to move in said channel toward saidroll.